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Engine difference between 4th gen and STI?


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I've been searching for a while, but I can't seem to find an answer. What, if any, differences are there between Legacy engines (2007 GT specifically) and STI engines? Are they the same short blocks with different throttle bodies, turbos, and intercoolers?
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There's a lot of discussion about this.

 

The external piece's seem to be the main difference. Last year I put a ej257 short block in my wagon using the gasket kit for my 05 ej255.

 

Some have talked about the pistons being different.

 

Really its not a big deal.

 

Here's my ej257

 

http://i185.photobucket.com/albums/x40/92Si/DSCN4652.jpg

 

here's the ej255

 

http://i185.photobucket.com/albums/x40/92Si/DSCN4754.jpg

305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD).  CHECK your oil, these cars use it.

 

Engine Build - Click Here

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Intake manifolds are obviously different, and dual ACVS heads vs single AVCS heads are another that I know of.

I thought something else in the heads were differnt too, maybe retainers?

Somebody will inow for sure, but IIRC, it seemed like the heads and intake manifolds were the big difference.

Self proclaimed PNW Craiglist find of the day Champion, April 2014.
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Cams are completely different, single AVCS on the EJ255 vs. dual AVCS on the EJ257, forged internals on the EJ257, IM, injectors, turbo, TMIC, EJ257 is a semi-open deck block where the EJ255 is an open-deck block, the list goes on lol.

 

The short blocks are swappable though :)

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Lots of misinfo in here. Both shortblocks are the same. Not all 257s had variable timing on the exhaust cams all years.

 

They both have forged rods, and cast pistons.

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Oh the dishes are different on the pistons. There have been some minor changes to both blocks over the years so that needs to be considered too.

 

Over the years there are some differences. But for 05 they are the same. Pistons included

USLegacy-1.thumb.jpg.9f5dc27ae942df7010247f1c04d8af90.jpg

USParts.thumb.jpg.6141fcf10abbc97b702b9e28d75a0e16.jpg

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EJ257's have forged cranks EJ255's don't... 2005 is the only exception for the bottom end being the same. Don't know how that makes them the same???
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Cams are completely different, single AVCS on the EJ255 vs. dual AVCS on the EJ257, forged internals on the EJ257, IM, injectors, turbo, TMIC, EJ257 is a semi-open deck block where the EJ255 is an open-deck block, the list goes on lol.

 

The short blocks are swappable though :)

 

EJ257's have forged cranks EJ255's don't... 2005 is the only exception for the bottom end being the same. Don't know how that makes them the same???

 

Just so no one gets confused, I highlighted the wrong stuff in Red.

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Thanks for all the information. I'm looking to replace my engine with a short block from a local builder (vigilant motorsports) and he uses a new STI short block. I just wanted to be sure they will mate up. Its not something I'll do soon, but I'm info gathering right now.
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No body mentioned that 07+ Legacy switched to D25 heads, which bumps up the compression ratio. If you are shopping for pistons, they are usually rated with the B25 heads. So if you see a stock replacement STI piston rated at 8.2:1, your CR will end up around 8.5:1.

IIRC, all EJ257 long blocks come with B25 heads.

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Well thank you for the correction BAC. Perhaps you can help me understand why it would be better to have a 257 bottom end than a 255 bottom end? I've always been under the impression that the 255 was not as strong and could not hold the same power/boost as the 257, leaving the heads aside.
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